The present invention relates to lung ventilation and, more particularly, to a method device and system suitable for monitoring lung ventilation.
In the medical treatment of patients requiring breathing assistance, it is common to insert an endotracheal or nasotracheal tube into the trachea of the patient, by way of the mouth, nose or any other surgically created opening. One end of the tube is connected to a ventilator which periodically forces air into the lungs through the tube. In big children and adult patients the inner end of the tube is typically provided with an inflatable cuff which is inflated by conventional means subsequently to the insertion of the tube into the trachea. In small children and neonates there is no cuff and it is impossible to fix the inner end.
It is recognized that the position of the tube within the trachea is of utmost importance because such tubes are necessary to ensure that a patient's lungs receive oxygen, and any misplacement of the tube, both during the intubation or during ventilation, can have dire consequences. Once inserted into the trachea, the naso- or oral endotracheal tube must offer continues and substantially obstacle-free ventilation path to both lungs. If inserted too deeply, the tracheal tube may enter one of the two main stem bronchi (typically the right) and direct air flow to and from only one of the lungs. Asymmetric or one lung ventilation also occurs due to displacement of the tube after changes in posture or following repositioning of the tube and development of heavy secretions (foreign body) in the big airways. Asymmetric or one lung ventilation may lead to the development of respiratory insufficiency and subsequent hypoxia, hypercapnia and acidosis. Furthermore, one lung inflation can cause hyperinflation of one side leading to pneumothorax at that side, and simultaneously can create atelectasis at the other side, leading to other complications as lobar pneumonia, and the like. Conversely, displacement of the tube to or above the vocal cords may result in insufficient ventilation and/or damage to the vocal cord.
Additional complications which may occur during ventilation are pulmonary barotraumas, such as pulmonary interstitial emphysema, pneumothorax and pneumomediastinum. Such barotraumas are caused by lung disease and/or high air pressure in the lungs which results in rupture of alveolar structures and lung tissue. In pneumothorax, air is present in the pleural cavity, and in pneumomediastinum air is present in the mediastinum.
Another complication which may occur during ventilation is deterioration in the gas supply, due to, e.g., malfunction of the mechanical ventilator, partial detachment of ventilator circuit, partial obstruction in the endotracheal tube by secretions, fluids accumulation, torsion, kink, and the like.
The above problems are aggravated when ventilation is performed to premature infants and patients suffering from severe parenchymal lung diseases such as respiratory distress syndrome (hyaline membrane disease or adult RDS), bacterial pneumonia, pneumonitis, viral pneumonia, meconium aspiration syndrome, and other.
Of particular challenge is the ventilation of neonate and premature infants, because the endotracheal tube is extremely small and any small displacement (within millimeters) can result in inappropriate ventilation. The endotracheal tube used for newborns is not anchored at the distal end using an inflatable cuff, and movement of the newborn and extension or flexion of the neck may displace the tube from the appropriate position. Serious life threatening complications can result from inappropriate ventilation. Pulmonary air leak, such as Pneumothorax, pneumomediastinum, pneumopericardium and pulmonary interstitial emphysema, may develop as a complication during mechanical ventilation in premature infants from excessive pressure ventilation, but may also develop spontaneously. A most dangerous complication is partial or full detachment of the endotracheal tube with ineffective ventilation. The associated hypoxia and hemodynamic changes induced are especially dangerous for the vulnerable premature newborn infant and can lead to intracranial (intraventricular) hemorrhage and to the development of severe irreversible neurological sequelae as a result of brain damage.
Over the years, several attempts have been made to devise techniques which prevent or minimize problems associated with inappropriate mechanical ventilation. These include, auscultation, air flow monitoring, end tidal carbon dioxide monitoring, transcutaneous monitoring of oxygen or carbon dioxide, pulse oxymetry, heart rate, respiratory rate, invasive and non-invasive blood pressure monitoring and periodic blood gas analysis, along with tight physical supervision of the staff.
For example, U.S. Pat. No. 4,296,757 discloses a respiratory monitor which includes a detector for detecting the expansion of the chest of the person and an alarm circuit coupled to the detector for producing an alarm signal if the detector does not detect expansion of the chest for a predetermined period of time.
U.S. Pat. No. 7,036,501 discloses apparatus for monitoring the carbon dioxide of a patient's breath. An airway is inserted into the throat, such that a proximal end of the airway is placed at the mouth and a distal end extends through the throat to the vicinity of the larynx. The airway includes a nipple connected to a suction device that can intermittently aspirate the throat of the patient and clears mucus to maintain the airway open for breathing. A conduit is connected to a carbon dioxide monitor that monitors the content of the exhaled breath of the patient at the end of the respiratory cycle.
U.S. Pat. No. 3,942,513 discloses a sensor which detects respiratory activity and converts the activity to electrical signals to feed an apnea monitor. Once respiratory distress problems are detected, the apnea monitor transmits signals indicative of apnea episodes to an alarm unit.
U.S. Pat. No. 6,168,568 discloses a system which includes a plurality of sensors placed around the respiratory system of a patient and a breath analyzer. The sensor measure breath related activity and produce breath sound data, and the analyzer matches the data to breath sound templates, were each of the templates parameterizes one type of breath sound. The analyzer thus determines the presence of regular and/or adventitious breath only when the sound data matches one or more of the sound templates.
Additional references of relevance include: U.S. Pat. Nos. 4,494,553, 5,775,322, 5,785,051, 5,957,861, 5,996,582, 6,064,910, 6,139,505, 6,261,238, 6,287,264, 6,315,739, 6,349,720, 6,423,013, 6,494,829, 6,584,974, 6,651,665, 6,701,918, 6,705,319, 6,715,491, 6,723,055, 6,765,489, 6,820,614, 6,837,241, 6,918,878, 7,094,206, U.S. Patent Application Nos. 20030139679, 20040267149, 20050192508, European Patent Application No. EP00956822, and Japanese Patent Application Nos. JP2002190372 and JP2004033254.
Traditional monitoring techniques, however, suffer from many limitations, including non-automated monitoring which requires tight physical supervision of the medical staff, frequent false alarms events, slow speed of detection, low sensitivity, particularly with thin tubes, low specificity and low sensitivity, particularly to the detection of pneumothorax or other complications associated with asymmetric ventilation.
There is thus a widely recognized need for, and it would be highly advantageous to have a method device and system suitable for monitoring lung ventilation, devoid of the above limitations.